Figure (PageIndex1) mirrors that we require 2 hydrogen atoms and also 1 oxygen atom to make onewater molecule. If we desire to make 2 water molecules, we will need 4 hydrogen atoms and also 2 oxygen atoms. If we want to make 5 molecules the water, we require 10 hydrogen atoms and also 5 oxygen atoms. The proportion of atoms us will should make any number of water molecules is the same: 2 hydrogen atom to 1 oxygen atom.

You are watching: What is the ratio of hydrogen atoms to oxygen atoms

Figure (PageIndex1) Water Molecules. The ratio of hydrogen atom to oxygen atoms offered to make water molecule is constantly 2:1, no issue how plenty of water molecules are being made.

Using formulas to suggest how plenty of atoms that each facet we have actually in a substance, we have the right to relate the variety of moles of molecule to the variety of moles that atoms. Because that example, in 1 mol that water (H2O) we can construct the relationships given in (Table (PageIndex1)).

Table (PageIndex1): Molecular relationship for Water 1 Molecule the (H_2O) Has1 Mol that (H_2O) HasMolecular Relationships
2 H atoms 2 mol that H atoms (mathrmdfrac2: mol: H: atoms1: mol: H_2O: molecules) or (mathrmdfrac1: mol: H_2O: molecules2: mol: H: atoms)
1 O atom 1 mol the O atoms (mathrmdfrac1: mol: O: atoms1: mol: H_2O: molecules) or (mathrmdfrac1: mol: H_2O: molecules1: mol: O: atoms)

The Mole is big

A mole to represent a very big number! The number 602,214,129,000,000,000,000,000 looks around twice as long as a trillion, which way it’s around a sunshine trillion.



A sunshine trillion kilograms is how much a earth weighs. If 1 mol of soldier were stack in a column, it might stretch ago and forth in between Earth and the sunlight 6.8 billion times.

Example (PageIndex1): Ethanol

If a sample consists of 2.5 mol that ethanol (C2H6O), how numerous moles that carbon atoms does that have?


Steps for problem Solving

If a sample consists of 2.5 mol that ethanol (C2H6O), how numerous moles that carbon atoms does it have?

Identify the "given" information and what the difficulty is questioning you come "find."

Given: 2.5 mol C2H6O Find: mol C atoms

List other well-known quantities.

1 mol C2H6O = 2 mol C

Prepare a principle map and also use the ideal conversion factor.

Cancel units and also calculate.

Note how the unit mol C2H6O molecules cancels algebraically.

(mathrm2.5: cancelmol: C_2H_6O: molecules imesdfrac2: mol: C: atoms1: cancelmol: C_2H_6O: molecules=5.0: mol: C: atoms)

Think around your result. There room twice as numerous C atom in one C2H6O molecule, therefore the last amount need to be double.

Exercise (PageIndex1)

If a sample consists of 6.75 mol the Na2SO4, how numerous moles of salt atoms, sulfur atoms, and also oxygen atom does the have?

Answer 13.5 mol Na atoms, 6.75 mol S atoms, and also 27.0 mol O atoms

The truth that 1 mol equals 6.022 × 1023 items can likewise be used as a conversion factor.

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Example (PageIndex2): Oxygen Mass

Determine the massive of Oxygen in 75.0g the C2H6O.


Steps for difficulty Solving

Determine the mass of Oxygen in 75.0g the C2H6O

Identify the "given" information and also what the difficulty is asking you to "find."

Given: 75.0g C2H6O Find: g O